Igtt] PRITCHARD—DISSEMINATION OF PUCCINIA 181 
under date of June 27, the uredospores of P. graminis were gen- 
erally present upon the spring wheat earlier than they were 
observed upon the wild grasses remote from the barberry bushes. 
In fact, P. graminis was present in the uredo stage upon spring 
wheat July 6, and with one exception could not be found upon the 
grasses remote from the barberry even July 9, after which date no 
further search was made for uredo upon the latter. 
Experiments were made to obtain data with reference to the 
spread of P. graminis from grasses to the wheat fields by means of 
the uredospores. Twenty-eight uredo pustules were selected 
from Agropyron tenerum, A. repens, Avena fatua, and Hordeum 
jubatum, and 230 plants inoculated. From each pustule inocula- 
tions were made upon plants of wheat, barley, rye, and oats, and 
upon the host species from which the rust was obtained. Parallel 
marks were made upon the leaves with India ink, and the spores 
placed between them in order to distinguish the results of regular 
inoculations from accidental infection. There was very little 
spreading of the rust, however, as the infected leaves were always 
removed from the greenhouse. The plants were covered with bell 
jars 24-48 hours, as formerly. Germination tests of the uredo- 
spores showed an average viability of 70-80 per cent. 
The uredospores of 21 of the 28 pustules caused infection, but 
showed a decided preference for certain host species. The rust 
readily infected rye, oats, and the grasses, but not wheat or barley. 
In fact, the results of the few experiments made seem to show 
what was anticipated from the two series of infection experiments 
with aecidiospores, viz., that one form of P. graminis is common to 
Hordeum jubatum, Agropyron tenerum, A. repens, Avena fatua, 
oats, and rye, but is incapable of infecting either barley or wheat. 
This furnishes little encouragement to those who believe that 
P. graminis is spread to the wheat fields from the barberry bushes 
or from occasional protected spots, as beneath ice by aid of the 
native grasses. The data however give no information with respect 
to the forms of P. graminis on wheat or barley, as neither was 
infected, but in our breeding experiments in 1905 a number of 
wheat plots were surrounded by a border of barley which was 
practically destroyed by black rust, and yet there was no visible 
